Acid-promoted hydrothermal on Chinese herbal residue toward upgradation and denitrogenation capabilities

Abstract

Chinese herbal residue (CHR) is an association of renewable resource and hazardous waste, and high nitrogen content and low energy density are two primary obstacles to its efficient and clean thermal utilization. In this paper, acid-promoted hydrothermal was employed to probe the feasibility on CHR toward enhanced solid biofuel concerning upgradation and denitrogenation. A more excellent hydrothermal promoter (H2SO4) was demonstrated to upgrade and denitrogenate CHR with better energy (1.125) and nitrogen densities (0.586) at optimal conditions (160 °C, 0.5 N H2SO4), which could be attributed to the improved removal of oxygen, amino and ash during acid-promoted hydrothermal. Compared to raw feedstock or the conventional hydrochar, the acid-promoted hydrochar had enhanced compositional characteristics with higher heating value (21.00 kJ·mol−1), lower nitrogen (1.44 wt%) and ash (11.03 wt%) contents, thus showing more stable combustion flame with a higher comprehensive combustion index of 4.861 × 10−8, a higher combustion stability index of 4979.342, lower combustion alkali index of 0.026, and less nitrogen gaseous pollutant emission. Thus, acid-promoted hydrothermal would be a promising way to convert CHR into much cleaner and higher-grade solid biofuel.